HONOLULU (AP) — Hawaii officials plan to spend the next two years studying tiger shark movements around Maui amid what they call an unprecedented spike in overall shark attacks since the start of 2012.

Chairman William Aila of the Hawaii Department of Land and Natural Resources said Tuesday that Hawaii waters are safe if swimmers are cautious. However, he said prevailing opinion is that there are more sharks and more people in Hawaiian waters, creating more chances for bites.

“We know that the impression is that there is an inordinate amount of shark attacks that have happened recently,” Aila said. “We just want to make it clear that within the history of the state of Hawaii, the number of shark attacks have gone up, and they’ve gone down, and there have been some years we’ve actually had no shark attacks.

There have been eight attacks statewide this year and 10 in 2012. Hawaii usually sees only three to four attacks each year, and saw one or zero attacks in 11 years between 1980 and 2012, according to state data.

A 20-year-old German tourist lost her arm in an attack last week as she snorkeled off the coast of Maui. Four days later, a 16-year-old surfer suffered injuries to both legs after a shark bite in waters off the Big Island. There have been four attacks in the last month, though it’s not clear what type of shark was involved in each incident.

During a news conference, Aila said Hawaii doesn’t know as much as it should about shark movements in waters around Maui and the Big Island. That’s why it’s planning a two-year study to tag and track tiger sharks, which will begin next month.

Dr. Carl Meyer, a marine biologist with the University of Hawaii, said the study will focus on tiger sharks because they move around frequently and have been known to travel all around the islands’ waters.

Meyer, who is leading the study, said tiger sharks can travel up to 100 miles in a day, don’t stay in one area very long and can swim in very shallow waters if they choose to.

Aila said the study will help determine if signs, closures or other measures are needed to minimize encounters between sharks and humans.